"O Fortuna" is a medieval Latin Goliardic poem which is part of the collection known as the Carmina Burana, written early in the 13th century. It is a complaint about Fortuna, the inexorable fate that rules both gods and mortals in Roman and Greek mythology.

In 1935–36, "O Fortuna" was set to music by German composer Carl Orff as a part of "Fortuna Imperatrix Mundi", the opening and closing movement of his cantata Carmina Burana. It was first staged by the Frankfurt Opera on 8 June 1937. It opens at a slow pace with thumping drums and choir that drops quickly into a whisper, building slowly in a steady crescendo of drums and short string and horn notes peaking on one last long powerful note and ending abruptly. The tone is modal, until the last nine bars. A performance takes a little over two and a half minutes.

Orff's setting of the poem has influenced and been used in many other works and has been performed by numerous classical music ensembles and popular artists. It can be heard in numerous films and television commercials, and has become a staple in popular culture, setting the mood for dramatic or cataclysmic situations. "O Fortuna" topped The People's Classical Chart in 2009 as the most-played classical music of the previous 75 years in the United Kingdom.